Problem: $ \left(\dfrac{64}{25}\right)^{-\frac{1}{2}}$
$= \left(\dfrac{25}{64}\right)^{\frac{1}{2}}$ Figure out what goes in the blank: $\Big(? \Big)^{2}=\dfrac{25}{64}$ Figure out what goes in the blank: $\Big({\dfrac{5}{8}}\Big)^{2}=\dfrac{25}{64}$ So $\left(\dfrac{64}{25}\right)^{-\frac{1}{2}}=\left(\dfrac{25}{64}\right)^{\frac{1}{2}}=\dfrac{5}{8}$